Hybrid and electric vehicles generally incorporate contactors for selectively connecting high voltage cells to the high voltage DC bus of the vehicle. The high voltage DC bus typically includes significant resistance and capacitance, both in normal use and when it is inactive. When the vehicle is started prior to commencing a journey, the high voltage DC bus will normally be fully discharged resulting in a significant voltage difference across the contactors. Closing the contactors in the presence of such a voltage difference can cause arcing across the contactor blades. This will cause heating and wear and can result in the blades being welded together.
One solution for preventing this issue is to precharge the high voltage DC bus prior to closing the main contactors, for example using a separate circuit that incorporates a series resistor on initialization of the vehicle. However, the precharging sequence heats the resistor and can cause damage if carried out several times in a short period of time.
In an effort to mitigate resistor damage, repeated attempts to initialize the vehicle may be prohibited. This prohibition may, for example, be implemented after a predetermined number of attempts within a given period of time. However, preventing initialization of the vehicle's onboard systems can cause significant inconvenience to the driver.
It is therefore a first non-exclusive aim of the invention to mitigate this issue. It is a further, more general non-exclusive aim of the invention to provide an improved means of protecting or preventing damage to the electrical circuits of a vehicle.